Uncovering new physics in metals manufacturing

For decades, it’s been known subtle chemical patterns exist in metal alloys, but researchers thought they were too minor to matter – or they were erased during manufacturing. However, recent studies have shown in laboratory settings these patterns can change a metal’s properties, including its mechanical strength, durability, heat capacity, radiation tolerance, and more.

Researchers at the Massachusetts Institute of Technology (MIT) found these chemical patterns also exist in conventionally manufactured metals.

“You can never completely randomize the atoms in a metal. It doesn’t matter how you process it,” says Rodrigo Freitas, the TDK Assistant Professor in the Department of Materials Science and Engineering.

Conventional wisdom says there’s a point where the chemical composition of metals becomes completely uniform from mixing during manufacturing. By finding that point, the researchers thought they could develop a simple way to design alloys with different levels of atomic order, also known as short-range order.

“The first thing we did was to deform a piece of metal,” Freitas explains. “That’s a common step during manufacturing: You roll the metal and deform it and heat it up again and deform it a little more, so it develops the structure you want. The thought was as you deform the material, its chemical bonds are broken and that randomizes the system.”

The researchers found during mixing the alloys never reached a fully random state. They discovered some standard chemical arrangements in their processed metals, but at higher temperatures than normally expected. They also found completely new chemical patterns the researchers referred to as “far-from-equilibrium states.”

The researchers built a model explaining how the chemical patterns arise from defects (dislocations) such as three-dimensional scribbles within a metal. As the metal is deformed, those scribbles warp, shuffling nearby atoms. Previously, researchers believed shuffling completely erased order in the metals, but they found dislocations favor some atomic swaps over others.

“These defects have chemical preferences that guide how they move,” Freitas says. “Given a choice between breaking chemical bonds, they tend to break the weakest bonds, and it’s not completely random.”

The researchers are now exploring how these chemical patterns develop across a wide range of manufacturing conditions. The result is a map linking various metal processing steps to different chemical patterns in metal. With this map, the researchers hope engineers can begin thinking of the patterns as levers that can be pulled during production to get new properties.

This work was supported, in part, by the U.S. Air Force Office of Scientific Research, MathWorks, and the MIT- Portugal Program.

Massachusetts Institute of Technology (MIT)
https://www.mit.edu